Synchronizer



S. G. BEST SYNCHRONIZER March 17, l1959 5 Sheets-Sheet 1 Filed Dec. 27, 1955 5 Sheets-Sheet 2 /NvENro/P STANLEY G. BEST BVM 4;' M

ATTURNEY March '17, 1959 s. G. BEST SYNCHRONIZER S. G. BEST SYNCHRONIZER March 17, 1959 Filed nec. 27. 1955 Y Mw 5 s if N NB R .t E 0 V60 T .m Nv. .T .r /EJYA t L M N. xuoh. M Y v. B,

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S. G. BEST SYNCHRONIZER March 17, 1959 5 sheets-sheet 4 Filed Dec. 27, 1955 S. G. BEST SYNCHRONIZER March 17, 1959 5 Sheets-Sheet 5 United States Patent O SYN CHRONIZER Stanley G. Best, Manchester, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application December 27, 1955, Serial No. 555,595

Claims. (Cl. 317-6) This invention relates to synchronizing mechanism for two or more devices and particularly to mechanism using pulse generators for synchronizing the rotation of propulsion devices such as aircraft propellers.

An object of this invention is mechanism including pulse generators driven by master and slave devices and in timed relation therewith to produce electric signals for controlling the speed of the slave and hence relative speed and phase of the two devices.

A further object is an improved pulse generator which will produce a short positive pulse once per revolution and which can be used in an electronic control to provide a speed and phase control to phase a slave with a master device.

A still further object is mechanism by which the relative phase of the master and slave may be adjusted by changing the governed speed of either the master or slave.

Further and other objects will be apparent from the following specification and claims and the attached drawings in which:

Fig. 1 is a block diagram showing onev master unit and one slave unit with provision for controlling other slave units by the master.

Fig. 2 is a schematic drawing showing a portion of the hydromechanical section of one of the propeller controls.

Fig. 3 is a portion of the electric circuit controlling the hydro-mechanical portion of Fig. 2.

Fig. 4 is a schematic wiring of the synchronizer and phasing portion of the electronic control showing how the output of one of the samplers is connected to the electric portion of the one control shown in Fig. 3.

Fig. 5 is a diagram showing the saw-tooth voltage wave from the wave former.

Fig. 6 is a diagram showing the voltage curve of the pulse from the pulse generators.

Fig. 7 is a diagram showing the voltage curve produced by the sampler and the type of signal fed by the phaser to the amplifier.

Fig. 8 is a diagram showing the signal produced by the oit-speed integrator and the type of signal fed by the off-speed integrator to the amplier.

In the operation of multi-engine aircraft it has beenV found desirable both from a vibration and a noise standpoint to not only synchronize the several engine-driven propellers but to also maintain a selected phase relation between the propellers. Mechanism responsive to speed alone is not capable of maintaining the required phase relation even when such mechanism is capable of maintaining fairly close speed synchronization.

Applicant has invented an improved device which may be used to control the speed of each propeller independently with the synchronizing mechanism disconnected or may be able to synchronize the several propellers and maintain a selected phase relation between them within comparatively small limits with the synchronizing mechanism connected. The propeller which has been chosen to explain the synchronizer mechanism is a propeller simi- V2-,878,427 Patented Mar. 17, 1959 ICC lar to that shown in Longfellow Patent No. 2,652,122. In this propeller type, a proportional solenoid energized by speed responsive mechanism, which may be of the type described in Patent No. 2,579,723, positions a valve controlling a servo motor mounted on a non-rotating support, which servomotor acting through a gear train positions a follow-up distributor valve on the rotating propeller hub to control the ow of hydraulic fluid to a hydraulic motor on the propeller to position the propeller blades in accordance with the position of the servomotor. The solenoid of the master and slave may be supplied with an exciting voltage from a respective frequency responsive speed selecting circuit and if phasing is desired, the slave may also be supplied with an exciting voltage from a speed and phase comparing mechanism comparing the speed and phase of the controlled propeller with the speed and phase of a master and providing an exciting voltage upon any variations of the slave speed and phase from that of the master. These latter speed and phase signals are, within limits, utilized to modify and override the speed signals from the frequency responsive circuit.

As shown in Fig. l, a master engine 10 drives a propeller 12. A single phase alternating current power generator 16 is driven by the engine 10 and its output is led to a frequency sensing device 18, which may be similar to the frequency sensing mechanism shown in application Ser. No. 261,020 of Thomas P. Farkas, led December ll, 1951, now Patent No. 2,772,378, in which the impedance of a circuit is designed to maintain the voltage drop in a portion of the circuit at a substantially constant value selected by speed selector 17 irrespective of frequency changes. This selected constant voltage is compared with the normal generator voltage, which varies with speed, to obtain a resultant signal or speed error signal, showing speed deviation from the selected speed. The speed deviation or speed error signal is red into an input box 19 and then into an amplifier 20 and after amplification is led to the proportional solenoid 22 controlling the servo mechanism to change the propeller pitch to return the propeller-engine speed to the speed manually selected by selector 17 in the frequency sensing device 18.

The slave propellers have identically the same mechanism as that described above for the master propeller and the path has been indicated in Fig. l for one slave by the same numerals as the master with the suix 61. Any desired number of slave propellers may be controlled from a single master. Fig. 4 shows how three slaves may be controlled. Only one slave is shown in Figs. l, 2, and 3 for purposes of simplicity, but it is believed to be obvious how others may be added. The slave propeller as shown in Fig. l is, however, in addition to the mechanism shown for the master, provided with a control device or synchronizer which will compare the speed and phase of the slave propeller with that of the master and supply a speed or phase error signal to the input mechanism 19a to bring the slave propeller speed and phase into synchronism with that of the master. Switches 136, as explained in more detail hereinafter, may be provided to select either propeller shown in Fig. l as the master, making the other propeller the slave.

rl`he speed control mechanism is effective over a control range of pitch angles, the lower limit of which is determined by a low pitch stop. Mechanism is provided for removing the stop under certain conditions at which time the speed control mechanism is disabled and control of the propeller is obtained through individual Beta control mechanism connected with the respective throttle control lever. The Beta control mechanism comprises a device for comparing the blade angle setting indicated by the servo potentiometer 24 with a blade angle selected by the Beta control 26 and feeding the resultant signal to the same input mechanism 19 which received the signal from the frequency sensing device of the speed control. The Beta control is used in starting and in reverse pitch to give a blade angle in accordance with the position of the respective throttle control lever. This Beta mechanism is explained in more detail hereinafter and in Farkass application Ser. No. 314,593, tiled October 14, 1952, now Patent No. 2,840,169.

Feathering may be accomplished by mechanically biasing plunger 27, Fig. 2, of the hydraulic mechanism of the propeller, to hydraulically move servo 23a thus overcoming the control of the servo 23a by the proportional solenoid to change the propeller pitch and feather the propeller.

Taking up the speed control in detail, the master and slave have identical independent speed control mechanisms but they will be explained for the slave propeller only because of the more detailed drawings thereof. The A. C. output of the power generator 16a, Fig. 2, is fed in on line 48a to the portion of the electronic governor shown in Fig. 3 and into a bridge having register 50 forming one leg of the bridge, resistors 52 and 54 forming another leg of the bridge, resistors 56 and 58a forming a third leg of the bridge and condenser 60 forming the fourthleg of the bridge. The A. C. voltage at the midpoint of the two sides of the bridge is passed through rectiers 66 and 68 respectively and their associated lter circuit to change the A. C. voltages to D. C., and the resulting D. C. voltages are compared at the junction 70 of resistors 62 and 64. The convention used in this application is that the arrows in the rectiers indicate the ow of current from plus to minus as distinct from electron flow. Any variation in speed of the power generator 16a from that selected by the setting of the variable resistance 58a will be indicated as a D. C. voltage at the junction 70 of resistors 62 and 64, the polarity and magnitude of the voltage being an indication of the direction and extent of the speed error. The speed error signal is led through line 72a, switch 74, and line 76 to the midpoint between resistors 78 and 80 in input box 19a and through to the vibrator 82 and to the amplifier indicated generally at 20a. As indicated in Fig. l, the speed setting resistor 58a is set by movement of the throttle control 84a connected with the selector arm 17a so that in order to change the speed setting ofthe propeller it is necessary to move the engine throttle. The direct current signal fed from input box 19a to the vibrator 82 is chopped into a square wave signal and amplified in amplifier 20a in a well known manner and after passing through a transformer 86 is again chopped by vibrator 88 operating in synchronism with vibrator 82 to provide a direct current output on line 90a to the proportional solenoid 22a, a portion of which current is led back through line 92 to form a negative feedback for the amplifier 20a. The servo potentiometer 24a shown in Fig. 1 is connected to a positive voltage in the power supply 95 by line 97 and the wiper of potentiometer 24a is connected by a line 94a and a condenser 96 and limiting mechanism 98 to a midpoint between resistors 100 and 102 to provide a variable sensitivity circuit forming the subject matter of patent application Ser. No. 517,544 led June 23, 1955 by C. B. Brahm, now Patent No. 2,849,072, to which reference may be made for further details as it is believed that a further description of this particular circuit is not necessary for a complete understanding of the present invention. As shown schematically in Fig. 2, proportional solenoid 22a controls pilot valve 104 to control the flow of fluid to one side of servo 23a. Servo 23a comprises a xed piston 106 and a movable cylinder S having oil at a constant pressure introduced to one side 110 from the main pumps 112 and having oil at greater or lesser pressure introduced to the opposite side 113 by the pilot valve 104. Mechanism indicated generally at 114 is used to supply pressure at a predetermined amount above and a predetermined tion. Movable cylinder 10S serves to actuate the servo potentiometer 24a to provide the variable sensitivity circuit when under speed control. As explained in more detail hereinafter, the same potentiometer is used to provide a blade indicating position when under Beta control. Cylinder 108 also actuates a shaft 116 having a set of blade angle switches 118 connected therewith. A low pitch lock ratchet 120 similar to pitch lock unit 268 in the Longfellow patent is also connected with shaft 116 which continues and drives the gear mechanism shown in more detail in the Longfellow patent and is the equivalent of shaft 168 of that patent. It should be suflicient for this application to state that shaft 116 through the gear mechanism actuates a distributor valve, not shown, in the propeller hub which has a follow-up mechanism connected thereto and serves in-a well known manner to position the propeller pitch in accordance with the position of the servo cylinder 108 so that each propeller pitch position corresponds to a predetermined position of the servo cylinder 108.

From the-above detailed description it will be apparentl that any variation in the speed of the power generator 16a and the propeller 12a which is geared thereto, from a speed selected by the governor setting mechanism 58a will result in an electrical signal at the junction between resistors 78 and 80 which will be amplified and fed to the proportional solenoid to actuate the-servo mechanism 23a and change the propeller pitch to change the power. generator speed and destroy the speed error signal which actuated the proportional solenoid, Ythus allowing the proportional solenoid to return to a neutral or on-speed position. This same action takes place independently in each of the propellers when they are connected for individual control, the speed of each propeller being controlled by its individual throttle lever 84 and the respective speed selector 58 connected thereto.

Phasing and synchronizing The signal limiting means shown and described in this application but not claimed herein is claimed in an application Serial No. 555,594 of Preli and Sims for Signal Limiting Means For Synchronizer filed on even date herewith.

Taking up the phasing and synchro-mechanism specifically, the pulse generator 14 of the master propeller 12 feeds a pulse signal into a saw-tooth former 28 which will transform the comparatively sharp pulse into a saw-tooth wave having a repetition rate in synchronism with the rotation of the propeller 12. In the now preferred construction, the pulse occurs once per propeller revolution, so that the saw-tooth occurs once per propeller revolution. The pulse from the pulse generator 14a of the slave propeller 12a is led to a sampler 30 to which the saw-tooth wave formed by the saw-tooth former 28 of the master is also led. By commutating the sawtooth wave of the master engine with the pulse from the slave engine, a signal is obtained indicating the direction and extent of out-of-phase position of the slave with respect to the master. This out-of-phase signal is fed to the input box 19a and thence to the amplier 20a and the proportional solenoid 22a and the servo mechanism 23a which being connected with the propeller 12a will change the propeller pitch in such a direction as to bring the slave propeller into phase with the master at which time the error signals will be cancelled and become zero.

In the event that the slave propeller is running at a speed different from the master such that the repetition rate of the slave pulse is continuously diierent from that of the master pulse or saw-tooth wave, provision is made for accumulating the voltage impulses resulting from the consecutive slave pulses by sampling opposite sides of the steep portion of the saw-tooth wave to thus provide a speed diierence signal which is also fed to the input box 19a to provide an additional signal to the proportional solenoid 22a to further change the propeller pitch to correct for this speed difference and bring the slave and master into synchronism.

These speed and phase signals within limits modify and override the speed signal from the frequency sensing mechanism so as to maintain an in-phase and synchronous condition with the master although the frequency sensing mechanism of the slave may be calling for a diierent speed from that of the master within a predetermined limit.

The pulse signals from which the saw-tooth wave is formed on the master engine and the pulse signal which is used in connection with the slave engine for coinmutating the saw-tooth wave are produced by pulse gener ators shown generally at 14 and 14u. The pulse generator (see Fig. l) comprises a permanent magnet 32 mounted to rotate with the propeller and to pass in close proximity to a horseshoe-shaped core 34 held against rotation by the engine 10. Core 34 carries a pair of coils 36 and 38, connected in series so as to add the voltages induced in the coils by the passage of the permanent magnet 32 past the coils. One free end of the coils is grounded and in the master the other free end of the coil is connected by wire 38 to the saw-tooth former 28. In the slave the other free end of the coil is connected by line 40 to the sampler 30. As shown in Fig. 4 line 38 from the master pulse generator leads to a saw-tooth former 28 having a transformer 42 for stepping-up the voltage of the pulse. The pulses are then led through electronic circuits including a tube 44 and a tube 46, similar to the tubes 55 and 50 of the Oiiner Patent No. 2,517,703, where they are transformed into a linear saw-tooth wave 14. The sawtooth wave is formed in a manner similar to that explained in the Oiner patent so that the following brief explanation of the saw-tooth former structure here is believed al1 that will be necessary.

The pulse developed by the master engine is coupled via condenser 205) to the signal grid 202 of the tube 44 which, with its associated circuit components, converts the pulses into waves having the desired saw-tooth forni.

Briey, condenser 204 is charged to a negative value close to the negative cathode potential of tube 44 when the positive portion of the pulse applied to condenser 200 causes the bias on the grid 292 applied through resistor 206 to be greater than cut oit. Resistors 208 and 210, forming a voltage divider from the negative voltage, say 130 volts, oi rectifier 212 place a negative voltage on the cathode 214 which is slightly positive with respect to the grid 202 so that the tube 44 is normally nonconducting. Capacitor 216 serves as a bypass to prevent any rapid changes in cathode current appearing as a bias on the tube. Condenser 204 is discharged through resistors 218 and tube 46.

Resistor 220 is a cathode resistor of tube 46 which is a cathode follower type of tube having a plate voltage, of say plus 200 volts, supplied by the rectifier 222. Resistors 224 and 226 establish the bias of the grid of the tube 46 so that the average current through tube 46 is constant and hence the voltage appearing at the junction of resistors 21S and 221) has some average constant value between minus 130 and plus 20G, say around zero volts. Hence condenser 264 will charge to some negative value of say 110 volts when tube 44 conducts and will be slowly discharged through resistors 218 and tube 46 to a voltage a fixed amount less than the voltage at their junction, say 70 volts less. vThe voltage across condenser 264 is shown by the curve of Fig. and is seen to be of the desired saw-tooth form. The current pulse through tube 44 causes a voltage across condenser 204 to drop from V1 of say minus 30 volts to V2 of say minus 110 volts. If the voltage at V2 is some fixed value, such as minus volts, the voltage of V2 minus V1 will not depend on the frequency. The reason for this is that the alternating component of the voltage on condenser 204 is applied to the grid of tube 46 through condenser 228. The average grid bias with respect to ground on tube 46 is held constant through resistors 224 and 226. Tube 46 acting as a cathode follower, the alternating voltage existing across its cathode resistor is only slightly less than across condenser 204. Therefore, the current flowing through resistor 218 will be small. If the average voltage across condenser 204 should tend to increase, that is, have a higher numerical negative value due to increased pulse frequency, there will be a large increase in the current through resistor 218 since the average voltage across cathode resistor 220 is constant. This increased current through resistor 218 will quickly charge condenser 204 until the average voltage returns practically to its original value. This will then piace the voltage at V1 at its former value so that V1 minus V2 is again the saine voltage and the amplitude of the wave remains substantially constant.

For any iixed frequency, condenser 204 will discharge at a constant rate due to a constant diierence between the cathode and grid voltages of the cathode follower tube 46. Discharging at this constant rate will provide a linear saw-tooth wave.

The linear saw-tooth voltage from the saw-tooth former 28 is led on line 122 to a sampler 30 having a circuit comprising tubes 124 and 126 and having the cathode of tube 124 and the plate of tube 126 connected to the saw-tooth input by line 122. The pulse from the pulse generator 14a of the slave engine is fed in on line 128 to a transformer 134) and thence to the grid of both tubes 124 and 126. A negative bias is normally maintained on both grids by the resistors 131 and 133 forming a voltage divider and connected into a minus 13() volt line. The positive portion of the pulse from generator 14a will cause one of the tubes 124, 126 to conduct and charge condenser and thus sample the saw-tooth voltage and place a resultant signal on the grid of tube 132 which will indicate the direction and extent of out-ofphase of the master with respect to the slave. The iixed grid bias on the grid of tubes 124 and 126 is so adjusted that no anode current can iiow through either tube, except when the positive pulse is applied to the grids from the slave pulse generator.

To explain the action of the sampling device, assume that condenser 13S has been charged so as to apply a positive voltage to the plate of tube 124, the cathode of and the grid of tube 132. If at the tine the positive pulse is applied to the grids of tubes 124 and 126, the saw-tooth wave from the master applied to tubes 124 and 126 is more positive than the charge on the condenser', then tube 126 will conduct, charging condenser 135 to a more positive value. While if at that instant the saw-tooth wave from the master were more negative or less positive than the condenser 13S, then tube 124 will conduct and reduce the charge on the condenser. Thus a phase difference voltage wave will be developed across an energy storage device such as condenser 135 as shown by the curve of Fig. 7. It is evident from Fig. 7 that the phase difference voltage at condenser 13S corresponds in polarity and magnitude to that of the saw-tooth wave at each sampling instant and is constant between sampling cycles and further is proportional to the phase difference at the start of each cycle. lf the frequencies of the pulses remain the same, and their phase relationship remains unchanged, condenser 135 will remain at that charged potential. Should the phase relationship change, the voltage across condenser 135 would assume a new value proportional to the phase relationship between the saw-tooth and the slave aereas? 7 pulse as shown in Fig. 7. No significant current will ow from condenser 135 to the grid of tube 132.

Further explanation of this sampling mechanism is believed vunnecessary here because this sampling mechanism is substantially the same as that shown in Otfner Patent No. 2,517,703 mentioned above to which reference may be made for a more detailed description. Tube 132 being a cathode follower type will, from the voltage at the upper end of resistor 148, give an indication in line 134 of the out-ofphase condition. As shown in Fig. 4, this out-of-phase indication is led through a master selector relay switch indicated generally at 136 to the output line 138:1 which as shown in Fig. 3, is connected to a midpoint between resistors 140 and 142 and also connected with lead network 144 and lag network 146. With the voltage existing at the upper end of resistor 143, fed to the proportional solenoid 22a so as to change the phase relation of the slave propeller to the master propeller in the proper sense, the phase change will reduce the voltage at the upper end of resistance 148 to zero, indicating on-phase, thus synchrophasing would be accomplished.

Actuation of master selector relay 232, Fig. 4, and switches 136 which are controlled by switch 233 will ground out lines 138a and 153s leading to input box 19a and connect the sampler 30 and oit-speed integrator with lines 138 and 153 leading to the input box 19 of the master, and at the same time unground lines 138 and 153. The impulse generator 14 is simultaneously disconnected from the saw-tooth former 28 and connected with the sampler 30 and the pulse generator 14a is disconnected from sampler 30 and connected with the saw-tooth former 28, so that the engine and propeller which were slave A are now the master, and the master will become a slave.

Switches indicated generally at 234 controlled by relay 236 are energized by actuation of the switch 238 to either the right-or left-hand position shown in Fig. 4 to unground on the sampler circuits and in effect connect in the synchronizer mechanism. When the switch 238 is on the midpoint, the relay 236 is de-energized and the switches are all actuated to ground out the several samplers and ofi-speed integrators and put the propellers all back under control by their individual governors alone. The value of resistors 140 and 142 is much higher than the value of resistors 78 and 80 through which resistors the off-phase and the slave speed error signals are combined so that grounding of the synchronizer circuits and resistors will not materially aiect the operation of the speed control acting through resistors 78 and 80.

O speed integrator' If the relative rotation of the propellers were to change by more than 180, an erroneous signal would be obtained, indicating that the propellers were off-phase in the opposite direction from that in which the correction was being made. In order to solve this problem, an off-speed integrator is supplied which will count the number of revolutions of oit-phase which exists and produce a signal proportional to that number to be applied to the amplifier and thus overcome speed setting misalignment. The olf-speed integrator utilizes a pulse 147, Fig. 7, produced by the rapid change in the sawtooth wave in the plate circuit of tube 132 and energizes cathode follower tube 150 to produce an ofi-speed signal in line 152. The signal in line 152 is fed through a selector relay 136 to line 153e and eventually combined with the oit-phase signal and fed to the amplifier 20a.

The operation of the off-speed integrator is best explained by assuming that a constantly increasing phase error exists between the slave and the master due to underspeed of the slave. The voltage across resistance 148 will then be saw-tooth in form, really composed of small steps whose frequency depends on the speed difference between the slave and the master, Fig. 7. At the 8 i end of each revolution of relative phase` there will be an abrupt change 147 from positive to negative in the voltage across resistance 148. The phase circuit would make no distinction between plus 180 and plus 540v However, the abrupt change in voltage will indicate the change every time it occurs. If a condenser is charged every time the abrupt change occurs and the Voltage did not materially leak ofi the condenser between changes; the voltage across the condenser would indicate the number of times and the direction the relative phase had gone through 180. if the phase were changing in one direction, i. e., the slave underspeeding, the charge on this condenser should continually be going positive to 'eiect an increase in speed, and if the phase were changing in the other direction, i. e. the slave overspeeding, the voltage across this condenser should continually be going negative to decrease the speed. This voltage could then be added to the ott-phase signal, and the effective range of synchrophasing could thus be extended.

In practice, it is found that the abrupt change occurring across resistor 148 is of the wrong sense to charge a condenser so that the off-speed and off-phase signal will add to accomplish the desired result.

The phase can, however, be reversed by utilizing the plate circuit of the cathode follower tube 132 by placing a resistance 154 in that plate circuit. For an underspeed of the slave the voltage change which would be positive across resistance 154 caused by the large negative going pulse to the central grid of tube 132 induced by the abrupt change in saw-tooth voltage, is coupled through condensers 156 and 158 to rectiers 160 and 162.` If the voltage change across 154 is toward plus, i. e., slave underspeed, rectier 162 will conduct and charge condenser' 164, to some higher (more positive) value than it had previously achieved. This increased (positive) potential will be applied to the grid of tube which has a plate circuit resistor 167. Each pulse charging condenser 164 is additive until a maximum is reached, and thus each additional charge drives the grid of tube 150 more positive to increase the current in cathode resistor 165 and cathode bias resistor 163 and increase the voltage in line 152. The potential at the cathode resistor 165 of tube 150 will, due to the cathode follower action, be almost that existing across the condenser 164. This positive cathode voltage is applied to the junction be'- tween resistors 166 and 168 which connects the junction between condenser 156 and rectier 160 with the junction between condenser 153 and rectifier 162 thus tending to maintain the charge on condenser 164. These resistors together with resistor 170 and resistor 174 serve to bias the rectiers 160 and 162 so that no conduction will occur in tube 150 except when a material change in voltage occurs at the plate of tube 132. The sizes of the condensers 156 and 158 are such, and the contact potentials of rectiiiers 160, 162 are such, that an abrupt and material change in voltage is required to make the rectifers conduct. Thus a slow change in phase between plus and minus 180 degrees will not charge condenser 164, but when the phase circuit goes through the 180 mark, an abrupt and material change will occur and charge condenser 164 to some new value.

The action for negative change, i.e., slave overspeed, at the plate of tube 132 is exactly the same except that all polarities of signals are reversed and rectier 160 conducts, biasing the grid of tube 150 to reduce the current ow and produce a more negative voltage in line 152 which will assist the voltage in line 134 in restoring speed and phase coincidence.

rThe o-phase signal in lines 134-13811 and the offspeed signal in lines 152-153a existing at the cathodes of tubes 132 and 150, respectively, are "combined in the input box 19a and fed to the vibrator 82 and to the amplifier 20a. The output of line 15311, after passing out of the limiter 176, Fig. 3, is connected to line 13811 where it joinsrresistor 178 leading to the junction between resistors 140 and 142 connected to the vibrator 82. Condensers 180 and resistor 182 of the lag network 146 serve as an integrator to obtain high static sensitivity by blocking the flow of D. C. signals to ground while stable control is still possible because of reduced dynamic sensitivity. This reduced dynamic sensitivity is necessary only when a large speed difference exists between the slave and master engines. During this condition, the voltage is changing rapidly and assumes a condition which resembles noise. This is because the offspeed integral soon reaches the limit of its capabilities which are determined by the voltages selected for offspeed integrator tube 150 and by the contact potential of the rectifiers 184. The rapidly changing off-phase voltage exists as a saw-tooth wave form, see Fig. 7. The condenser of the lead network 144 and condenser 186 will pass these rapidly changing signals which become a series of pulses. The rectitiers 188 and condenser 190 act as limiters, preventing these pulses from reaching the electronic governor in any value over the contact potential of the rectifiers 188 plus whatever charge there may be on the condenser 190. The action of this limiter is different from that of a condenser alone, due to the contact potential of the rectifier 188. A denite mag nitude of voltage is required before the limiting will occur. Any steady state voltage existing across the limiter will charge the condenser 190 so that dynamic limiting will occur about this condenser voltage.

It is desirable to limit the effect of the off-speed integrator so that in the event the master should fail, the off-speed integrator or syncbronizer can carry the slave engine down below the slave governor setting only a small percentage, preferably of the order of 3%, of the speed setting of the slave engine governor and will not run the slave engine speed down to zero. This limiting of the amount of speed change of which the synchronizer circuit as a whole is capable may be achieved by selecting the operating voltages of the speed integrator cathode follower tube 150. By selecting the correct voltages for that tube, it cannot be driven suciently to cause more than a few percent change in speed. Any attempt to drive it further results either in cut-off or saturation of the cathode follower. It is preferred, however, to provide this limitation in the effective value of the off-phase and off-speed signals by means of the contact potential of the rectifiers 184 so that any potential produced in the off-speed integrator above a preselected amount will be shunted to ground. In order to provide the desired sensitivity the maximum off-speed and o-phase signals lbecome of a magnitude such that a dangerously large change in slave speed, say or more, is required to provide a balancing speed error signal. By limiting the voltage which the off-speed integrator or the phasing mechanism can apply to the junction of resistors 140 and 142 and thus to the amplifier 20, a limit is established for the off-speed signal which must be supplied by the frequency sensing governor 18a to the junction of resistors 78 and 80 to be combined with the off-phase and off-speed integrated signals on their way to the amplifier 20` to oppose and balance or reduce to zero the effect of off-speed integrated and off-phase signals. It will be understood that starting with the frequency sensing governor in an onspeed condition and putting out zero volts to the amplifier 20, if the synchronizer with its off-phase or off-speed signals were to drive the slave to a different speed such a dilerent speed would be an error in speed to the governor and will result in an opposing signal from the frequency sensing governor. Hence, by limiting the voltage which the off-speed integrator is capable of supplying and thus the governor speed error signal necessary to be combined with the off-speed integrated and off-phase signals to neutralize the integrator signal and stop further pitch change, it is possible to limit the extent of the offspeed excursions of the slave in its attempt to follow the master. The rectifiers 176 are inserted to prevent any slight voltage variations of the oit-speed integrator tube from entering the control system. The rectifiers 176 require the tube 150 to provide a signal which is greater than its output for synchronous operation but less than its output for a single pulse of off-speed before that signal can be conducted to the combining network.

While the specific values of the several elements may vary in different applications and persons skilled in the art would select values which most clearly accomplish the desired results for the particular installation, in order to help understand the invention, the following is a list of values for resistors and condensers which were used in a successfully operated device:

Resistor: Value Resistor: Value Tube or recti- 1 Selenium rectifier.

From the above description it will be observed that each of several, say four, propellers have been provided with speed control mechanism whose speed setting is determined by each individual throttle setting, the speed setting increasing with increasing throttle opening. Synchronizing and phasing mechanism has been provided comprising one saw-tooth wave forming device connected with the master propeller and three sampling devices, one for each slave propeller. The sampling devices compare the phase of the respective slave propeller with that of the master by sampling the master saw-tooth wave to provide a phase error signal and also count the revolutions of speed difference to provide a speed error integrated signal. The phase error and the integrated speed error signals are combined to provide a speed correction action to the slave propeller pitch control and restore iti-phase operation.

The above described synchronizer and individual governor control will control down only to a low pitch position determined by a mechanical low pitch stop 244. Operation below this low pitch stop position 244 to a starting or idling position and even down to reverse position is controlled by a Beta control device which is essentially a potentiometer 26 positioned by throttle lever 84 and a potentiometer 24 positioned by the propeller -blades 12 or servo mechanism 23. These potentiometers are connected to provide a signal to the ampliiier such as 20 through the resistors 78 and 80 to provide a pitch changing signal such that the propeller pitch will follow the movements of, and in effect be positioned by the throttle lever 84. The throttle is arranged so as to reduce the throttle opening down to a starting or idling position and arranged so that continued movement in the same direction will increase the throttle opening as the propeller moves into reverse pitch position. When the power lever is placed anywhere between idle and full reverse, a Beta switch 250 is closed. This switch supplies 28 volts ships supply to energize the Beta solenoid 252, Fig. 2. This will connect high pressure oil from the pumps 112 to the piston 254 to remove the mechanical low pitch stop lock for low pitch stop 244. Removal of the low pitch stop 244 will close switch 256 to conneet the 28 volts ships supply to one side of the Beta relay 240, the other side of which is connected through line 260 with a Beta arming switch 118 which is closed at all blade positions below a predetermined pitch above the low pitch stop position. Energizing the Beta relay, as indicated above, switches the input of the ampliier which is used for governing from the speed error signal to a blade angle error signal. As indicated above, the blade error angle signal is obtained -by comparing the outputs of a blade actuator potentiometer with a throttle lever actuated potentiometer. The throttle lever actuated potentiometer in effect shifts the ground connection for an otherwise ungrounded output portion of the power supply to thus in effect, change the value of the negative voltage of the power supply to the potentiometer. Actuation of the Beta solenoid 252, Fig. 2 will, in addition to removing the low pitch stop 244, also actuate piston262 and lever 264 to disable the overspeed governor 266 so that the propeller will not inadvertently increase pitch in the reverse pitch position.

Manual feathering is initiated by pushing valve 27, Fig. 2, to drain oil from one side of the servo cylinder and shut ofl pressure oil not required for the feathering operation. To top off the feathering operation, vthe auxiliary pump 268 driven by electric motor 270 is actuated to supply oil as the main pump 212 slows down.

Unfeathering is obtained by allowing valve 27 to return to the position shown in Fig. 2 and energizing the auxiliary motor 270. Ship power of 115 volt 400 cycles will supply the power for underspeed signals to the amplifier and proportional solenoid until the generator 16 provides sufcient voltage to operate solenoid and shift the power source to the respective generators and the control to the electronic governors.

It is to be understood that the invention is not limited to the specic embodiment herein illustrated and described, but may be used in other ways without departure from its spirit as deiined by the following claims.

I claim:

l. A governor system for a plurality of independently rotating propellers to be maintained in a predetermined phase relation, comprising an electric pulse generator driven by each propeller and creating an electric pulse in timed relation with the rotation of the respective propeller, means transforming the pulse from one generator into a saw-tooth type wave, individual sampling means for each of the other propellers, comprising means utilizing the pulse of each respective other propeller for sampling said saw-tooth wave and producing for each other propeller an individual signal varying in polarity and magnitude with the value of the saw-tooth wave at the moment of sampling, and means responsive to said individual signal for adjusting the speed of the respective propeller to phase the respective propeller with the propeller driving said one generator and eliminate said signal.

2. A device as claimed in claim 1 in which each pulse generator comprises a magnet and a coil arranged to pass in close proximity once per revolution of the driving device and produce a positive peaked pulse.

3. A device as claimed in claim 2 in which the magnet is a permanent magnet mounted on a rotating part of the driving device `and the coil is mounted on a nonrotating part of the driving device.

4. In a phasing mechanism for a master and a slave device, each having an individual speed governor, means for manually selecting the speed setting of each governor for controlling the speed of its respective device, means producing an oli-phase signal responding to the direction and extent of the phase dilerence between the master and the slave, means producing an oli-speed signal for each revolution of the slave relative to the master, means combining said off-phase and said ott-speed signals to pro-` vide a iirst speed error signal biasing said slave governor to restore synchronisrn, means producing a second speed error signal by a speed variation between said slave device and the slave governor speed setting, means cornbining said two speed error signals to produce a balanced condition with the master and slave operating in synchronism with the phase of slave displaced from that of the master and producing an oli-phase signal proportional to said phase displacement which is balanced by said second speed error signal proportional to the dif--I ference between the master speed and the slave governor setting, said phase displacement being controlled by said manual governor speed selecting means.

5. `In a phasing mechanism for a master and a slave device, each having an individual speed governor, means for manually selecting the speed setting of each governor for controlling the speed of its respective device, means producing an off-phase signal responding to the direction and extent of the phase difference between the master and the slave, means applying said off-phase signal to said slave device to change the speed of said slave device, means responsive to a speed variation between said slave device and the slave governor speed setting producing a speed error signal, means combining said speed error and said off-phase signals to produce a balanced condition with the master and slave operating in synchronism with the phase of slave displaced from that of the master and producing an olf-phase signal proportional to said phase displacement which is balanced by said speed error signal proportional -to the difference between the master speed and the slave governor setting, said phase displacement being controlled by said manual governor speed selecting means.

References Cited in the le of this patent UNITED STATES PATENTS 2,433,432 Chillson Dec. 30, 1947 2,482,812 Treseder Sept. 27, 1949 2,517,703 Olner Aug. 8, 1950 2,696,269 Chilman Dec. 7, 1954 2,747,141 Hine May 22, 1956 

